The present investigation is an attempt to assess the strength of cortical bone structure in vivo through the utilization of three independent measurements made on normals and patients. One is a photon absorption technique, which determines the bone mineral content (grams of bone/running cm.) of the bone. The second is the measurement of the speed of ultrasound (Craven, et al., 1973) through the transverse direction of the cortical bone. The third is a radiograph of the bone to determine the cortical thickness and overall radius. Through the use of these methods, quantitative measurements of the bone mineral content and the speed-of-sound are obtained. In addition, with the use of a bone model (Greenfield, 1973; Huddleston, 1973) additional properties, e.g., modulus of elasticity, compact bone density, bone mineral density, and percent ash content, can be derived. These properties have not been easily investigated by other means in vivo. These values will provide a more comprehensive index of the nature of bone structure than has been previously determined. Results have been obtained from a normal population of 44 volunteers and a patient population of certain disease states (osteoporosis, renal disease, degenerative arthritis, and rheumatoid arthritis) of comparable number. The ages ranged from 20-87 years. There is strong evidence that many of the derived values are strongly correlated to the nature of the bone structure and therefore to the health of the individual. The purpose of the proposed research is two-fold: 1) the validation of the derived properties of the bone obtained through in vivo measurements with values obtained by standardized in vitro engineering techniques performed on the same bone sample, and 2) continuation of the accumulation of data to obtain the range of values in a normal population for both males and females as a function of age. Upon completion of these studied, they may then be used to help diagnose an individual patient's bone health and/or to check the efficacy of the therapy being performed.